1. Field of the Invention
The present invention relates to a universal USB power supply unit, and more particularly, to a power supply unit utilizing the DC power supplied through the universal serial bus (USB) port by means of a feedback control voltage output circuit for use of PDAs, game machines, walkmans, etc.
2. Description of the Prior Art
The photoelectric, communication and digital technology have been rapidly developed so that PDAs, digital cameras, mini CD-ROMs, game machines and mobile phones have been very popular in the everyday life. Besides, the volume thereof becomes smaller and smaller to facilitate carrying so that they have been regarded as necessities of everyday life. However, when the battery runs down, it has to be recharged for further use. Moreover, the charger of each product requires different voltage. For example, the charging voltages of the mobile phones of Motorola, Nokia, Ericsson and Panasonic are different. Some need direct current of 4.2V and the others need 4.5V. And the other products like PDAs or digital cameras have the same problems as well.
When the user of these products goes on a (business) trip, a certain adapter and charger have to be taken with him for charging. However, to carry these accessories is very inconvenient. Moreover, different mains sockets are used in different countries so that special connectors are necessary, thereby resulting in much difficulty.
Now, the use of the computer is very popular, and most of the current computers have USB port which features 5V voltage output. Moreover, the specification of the output interface of most computers is identical. Particularly, the USB port of the laptop computer becomes a necessary accessory. In addition, USB port includes its own protection and voltage-stabilizing circuit. How to utilize the laptop computer to supply power is the main topic of the present invention.
The commercially available charging cable (A), as shown in FIG. 1, includes a USB port connector 1 at one end thereof while the other end thereof has a charging connector 2. In use, both ends of the charging cable (A) are respectively connected to the mobile phone and the computer for charging the battery of the mobile phone (M). However, the output voltage of the USB port is 5V DC voltage, and the required charging voltage of most mobile phones are different. Some of them even have difference of few volts. Accordingly, a harmful influence upon the charging effect and the battery life will be created when all kinds of batteries of the mobile phones are charged with the 5V voltage.
In order to remove the above-mentioned drawbacks, another charging cable (B), as shown in FIG. 2, includes a DC transformer 3 between the USB port connector 1 and the charging connector 2 in order to transform the 5V output voltage of the USB port to the charging voltage (for example: 3.8V) of the battery of the mobile phone (M). Though this supplies the constant required voltage to the mobile phone for charging, the charging cable (B) can be used for only one model of mobile phone, and is not applicable to another mobile phones or electronic products. In addition, the old models of the mobile phones are eliminated very fast. When the old mobile phone is replaced with a new one, a new charging cable (B) is necessary, thereby causing unnecessary waste. Besides, the same company produces different models of mobile phones so that charging cables (B) with different output voltage are necessary. Both connectors of the charging cable (B) has simple configuration and is cheap while the integrated circuit and electronic components inside of the DC transformer 3 are expensive. When the whole charging cable (B) is often replaced, it doesn""t meet the economic efficiency.
Furthermore, when the power source from the laptop computer is used to charge the batteries of the portable PDAs, digital cameras, etc., another charging cables are required. Generally, the charging voltages thereof are different. Therefore, it""s still impractical to utilize the USB port to charge the batteries of the portable PDAs, digital cameras, etc.
It is a primary object of the present invention to provide a universal USB power supply unit which can be utilized to offer different output voltages in accordance with different products for reaching the multifunctional effect. It is another object of the present invention to provide a universal USB power supply unit which is convenient to carry and easy to connect.